A Longing for My Venge Turns Up Some Intriguing Cycling Aerodynamics Information.

bgddyjim

2 years ago

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It’s the middle of January. When I walked out the door this morning it was 12 degrees, and sadly that’s with an F after it, not the balmy C. Yesterday morning it was so cold, snot froze instantly when I walked out the door.

My beloved Venge, sits waiting and ready in our (my wife and my) bedroom next to my wife’s Alias (the feminine version of the Venge). The Venge got brand new cables and a new chain this off-season so when the temp tops 50, it’ll be like riding a brand new bike again.

A Venge isn’t for everyone, of course. By today’s standards she’s a bit of a brute. It’s a stiff bike, by comparison. One of the stiffest on the market but that statement of reality is a little misleading. Comparing it in terms of comfort to my old 5200 isn’t a even fair fight. The 5200 is impossibly stiff in all the wrong places by comparison.

The Trek, with its 16 year-old technology, has a relatively small bottom bracket area while the Venge is all ass. The chain stays are squared sturdy as well, compared to the Trek’s thinner tubes. The trick is in the seat stays; thin blades where the Trek has thicker, tapered tubes. The Venge offers just a little “give” here to smooth out the road (at least that’s how it translates to my butt).

The fork on the Trek uses tubes, the Venge, blades. A tube for the head tube compared to a tapered, sculpted head tube, a tube for a seat post compared to a blade, etcetera, etcetera. The leap in comfort is much like the leap from an aluminum bike with a steel fork to the carbon fiber Trek. To say it’s profound is an understatement, and I can speak with experience on this because I’ve put considerable miles on all three types of road bike. I own one of each.

In simple terms, when it’s all said and done, the Venge feels like a Vette while the 5200 is more like a Camaro. Heavier, slower and a little less comfortable. This time of year, because I won’t hook the Venge up to a trainer, I always long for those summer days, bombing down the road, without the bulky winter clothing, feeling like I’m sitting on a bolt of lightening.

So I was cruising the interwebz last night searching with Google for Venge stuff and I happened on an article written about an interview of a person who works for the software company that did the fluid dynamic software for the Specialized McLaren Venge (Mclaren apparently uses their software as well). The Venge stuff is kinda cool, but this is what caught my eye”

Consider that the typical drag coefficient (a non-dimensional quantity that is used to quantify the drag or resistance of an object in a fluid environment) of a professional cyclist crouched on top of a moving bicycle ranges between 0.7 and 0.9. Assuming that the bicycle is highly efficient and the rider is aerodynamically streamlined, let’s estimate the Cd to be 0.83 and his/her frontal area to be 3.2ft2. If we consider that the rider is traveling at 20mph he/she feels approximately 3.27 pounds force from the aerodynamic loading acting to slow him/her down. In comparison, a typical touring bicycle and upright rider with a Cd of 1.0 and a frontal area of 4.3 ft2 feels approximately 4.4 pounds force at 20 mph[i].

Based on the aerodynamic effects and accounting for minor differences in rolling resistance, the touring rider must put in approximately 27 percent more horsepower to keep pace with the professional rider and bicycle.

So let’s look at this in terms of watts. On our normal Tuesday night club ride, when we’re pushing out 28-30 mph, we’re putting out around a normalized 250 watts (normalized means you average it out, you take out the 400 watt peaks and the 100 watt valleys). For a person on a touring rig, they would have to put out a whopping 342 watts, normalized, to keep up. But it’s worse… That 27% is good at only 20 mph. As speed increases, drag does exponentially, so that 348 is likely closer to 400 by the time you hit 28. My friends, that’s Jens Voight territory right there. And you ain’t Jens Voight.

Nor am I, but I’m not one of those who try to convince everyone that the setup of a bike doesn’t matter much. In any event, while I can’t possibly ride in the same position as a 30 year-old (let alone a 20-something) professional cyclist, it obviously pays to minimize that frontal area as much as possible.